Method for operating a motor pump

ABSTRACT

The method is provided for operating a pump unit with a centrifugal pump which is driven by an electric motor and which comprises a rotor ( 11 ) running in a split tube ( 10 ). The rotor space ( 17 ) is separated with respect to the stator ( 9 ) in a fluid-tight manner. On running the motor to its operational rotational speed the fluid located in the rotor space ( 17 ) due to the increasing rotational speed evaporates and is removed so that the motor finally functions as a dry-runner.

BACKGROUND OF THE INVENTION

[0001] The invention relates to a method for operating a pump unitaccording to the features specified in the preamble of claim 1, as wellas to a pump unit according to the features specified in the preamble ofclaim 3.

[0002] Centrifugal pump units of a smaller or average power which todayare part of the state of the art are usually designed as wet runners,i.e. they comprise a split tube which seals the rotor space with respectto the stator space, in particular, from the penetration of deliveryfluid. The delivery fluid located in the rotor space in particular alsoserves for the lubrication of the bearings carrying the rotor shaft. Thepumps of this construction type have proven themselves since they do notrequire any seal to the region of the movable parts, the rotor space maythus be conductingly connected to the pump space.

[0003] On the other hand, from the state of the art it is also known toapply dry runners, i.e., to seal the shaft carrying the pump impellerwith respect to the motor. In order here to seal the rotor space withrespect to the delivery fluid in a reliable manner and over a long time,one requires complicated sealing designs which are expensive and areoften prone to wear.

[0004] Although the dry runners are basically superior to the wetrunners with regard to efficiency since the distance between the rotorand the stator may be reduced and the magnetic field between thesecomponents is not weakened by the split tube, the extra expense forseals and the maintenance which is also required for long-term operationis so large that at least with small or average construction sizes onealmost exclusively uses wet running motors. Otherwise one must ensurethe permanent lubrication of the bearing.

[0005] In order to increase the hydraulic power of such centrifugalpumps and their efficiency, it is known to allocate a frequencyconverter to the unit, which is connected in front of the electric motorand permits a practically infinitely high rotational speed of the motorindependently of the mains frequency and voltage. With an increasingrotational speed however the fluid friction between the rotor and splittube becomes noticeable so that with this construction type an increasein the rotational speed beyond certain limits is not very useful.

BRIEF SUMMARY OF THE INVENTION

[0006] Against this state of the art it is the object of the presentinvention to create a method for operating a pump unit with which anoperation of the pump is possible at high rotational speeds.Furthermore, a pump unit according to the known type is to be designedsuch that it may be operated at high rotational speeds without havingthe initially outlined disadvantages of the two systems (wet runner/dryrunner).

[0007] The part of this object with regard to the method is achieved bythe features specified in claim 1, the part with regard to the device isachieved by the features specified in claim 3.

[0008] Advantageous formations of the invention are indicated in thedependent claims, the subsequent description and the drawings.

[0009] The basic concept of the present invention is to operate awet-running motor such that, although this may be designed as a wetrunning motor with regard to its construction type, it however has theproperties of a dry runner in operation, in particular it runs withoutthe liquid which is usually located in the rotor space with wet-runningmotors. By way of this, the design advantages of the wet-running motorwhich requires no complicated seals between the pump and the motor maybe retained without having to do without characteristics of a dry runnerwhich are particularly advantageous at high rotational speeds. Theinvention thus envisages at least partly removing the fluid located inthe rotor space before during and/or after running up the motor. At thesame time the fluid located between the rotor and split tube ispreferably evaporated by way of the effect of heat. It is indeedprecisely in this region that the removal of the fluid is particularlyimportant since it is here that the greatest friction output arises onaccount of the high relative speeds between the rotor and split tube.

[0010] Numerous design variants are possible for the construction withregard to the device for operating a pump unit. This may be achievedwith a particularly simple design and thus inexpensively in that therotor space is sealed with respect to the delivery fluid in apressure-limited manner. Such a pressure-limited sealing is sufficientin order to keep the rotor space largely free of fluid during operation.At the same time the design does indeed envisage the rotor space beingfilled with fluid before the start of the running of the motor. Thefluid however is indeed removed from the rotor space either by way of avalve specially envisaged for this, by way of a seal only effective upto a certain pressure or by way of other suitable means in that onaccount of the heating the fluid evaporates and thus the volume isincreased. By way of this the pressure rises until the pressurelimitation of the rotor space is exceeded and the fluid located hereescapes, be it in gaseous or liquid form. The vapor pressure which thenprevails here at the same time leads to the fact that no furtherdelivery fluid enters the rotor space. Also the pump design may beadvantageously envisaged as with a wet-running motor so that inparticular the fluid-lubricated sliding bearings favorable for highrotational speeds may be applied.

[0011] In order to be able to ensure the supply of the bearings withfluid also if the rotor space is largely free of fluid at operationalrotational speed of the motor, the invention envisages arranging thebearing carrying the rotor outside the rotor space. At the same timehowever at least one bearing carrying the rotor, preferably thatfurthest from the pump impeller is arranged within the split tube sincethen a fluid supply may take place via the central shaft bore and thus alargely axial pressure compensation on the shaft may take place.

[0012] It is favorable if both shaft ends are led out of the rotorspace, wherein then an impeller is provided at one shaft end and thefluid to be led away out of the rotor space may be led away near to thatend of the shaft distant to the impeller. Specifically as previouslyoutlined, if a pressure compensation exists via a shaft bore or anotherconduit connection, the removal of the fluid from the rotor space may beeffected almost without pressure and need not be effected against thedelivery pressure of the pump. Such a removal is particularly simplypossible with a conduit connection through the shaft, thus if this endof the shaft is impinged by the pressure of the suction side of thepump.

[0013] Axial face seals are preferably applied as pressure-limitedsealing means, wherein the setting of the pressure limitation iseffected by selection of a suitable spring with which the axial faceseal ring is held in contact.

[0014] It is useful if the axial face seal in each case is arrangedbetween the rotor and the adjacent bearing, wherein the bearing receiverfor the bearing removed from the impeller is seated within the splittube. At the same time, the bearing receiver is usefully sealed withrespect to the split tube by way of an outer seal and with respect tothe stationary part of the axial face seal by way of an inner seal.

[0015] In order to be able to remove fluid as completely as possiblefrom the rotor space it is useful either for the bearing receiver or theaxial face seal to bear at the end-face on the rotor with play or forthere to be provided a separate displacement component between thebearing receiver and the rotor which reduces the free volume between theend-face of the rotor and the bearing receiver, said volume being ableto be filled by fluid on operation. This displacement component isusefully manufactured of heat-insulating material, preferably plastic inorder to prevent the heat deliberately produced in the rotor space forevaporating the fluid located here from being led away at the end-face,or to prevent condensation arising in this region. For this reason it isuseful to also manufacture the bearing receivers from a heat-insulatingmaterial.

[0016] In order to achieve as quick and complete as possible evaporationof the fluid located in the rotor space it may be advantageous to designthe split tube heatable at least in a part region. In principle theproduction of heat may be effected by friction in the region between therotor and the split tube so that the fluid is automatically heated onrunning up the motor and is thus evaporated. To supplement this or forevaporation, one may however also provide a heating of the split tubebefore the start of the motor, be it due to an electrical resistanceheating or also inductively, in particular on account of the magneticfield formed on operation between the rotor and the stator. As a motorit is particularly advantageous to apply a permanent magnet motor.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The invention is hereinafter described in more detail by way ofan embodiment example shown in the drawing. There are shown in:

[0018]FIG. 1 a longitudinal section through a centrifugal pump unitaccording to the invention and

[0019]FIG. 2 the detail 11 in FIG. 1 in an enlarged representation.

DETAILED DESCRIPTION OF THE INVENTION

[0020] The pump unit shown in the figures comprises a housing 1 of around cross section on whose lower end-face there is formed asuction-side inlet 2 and on whose upper end-face there is formed apressure-side outlet 3. The fluid to be delivered is suctioned at theinlet 2, from here reaches a suction opening 4 of an impeller 5 of thepump from which it goes radially outwards into an annular channel 6 tothe outlet 3.

[0021] The channel 6 is delimited at its outer side by the housing 1, onits inner side by a motor housing 7 which is fixed within the housing 1.The electrical supply of the unit is effected by an electricalconnection 8 which is led laterally out of the motor housing 7, passesthrough the channel and is led out of the housing 1. The motor housing 7accommodates a stator 9 which is limited on its inner side by a splittube 10. Within the split tube 10 there runs a rotor 11 which is seatedon a shaft 12 which near to its ends is mounted in sliding bearings 13,14 which are seated in bearing receivers 15, 16 fixed within the splittube 10 and thus within the motor housing 7.

[0022] The split tube 10 radially delimits a rotor space 17 which at theend-face is limited spatially and in a pressure-limited manner withrespect to the remaining split tube space by way of axial face seals 18,19.

[0023] The shaft 12, which is mounted within the sliding bearings 13 and14, at the lower end carries the impeller 5 and also the rotor 11. Itcomprises a central passage hole 20 which forms a conducting connectionbetween the suction opening 4 and the upper end of the motor housing 7which in FIG. 1 is at the top. Since the shaft 12 is not sealed withrespect to the pump space as is usual with wet-running motors, the upperbearing 13 via the bore 20 and well as the lower bearing 14 is suppliedwith delivery fluid. With this the delivery pressure of the pumpprevails at the lower bearing 14, whereas the suction-side pressureprevails at the upper bearing 13. The rotor space 17 is sealed withrespect to the split tube space filled with fluid on operation only viaaxial face seals 18 and 19. The construction of such an axial face sealis represented by way of the upper axial face seal 18 in FIG. 2.

[0024] The axial face seal 18 consists of a stationary axial face sealring 21 which is incorporated within the component forming the bearingreceiver 15, is radially sealed with respect to this by way of an O-ring22 and is displaceably mounted in the axial direction of the shaft 12.This stationary axial face seal ring 21 is impinged with a pressureforce by a helical spring 23 surrounding the shaft 12. The helicalspring 23 is likewise arranged within the component forming the bearingreceiver 15. This annular space formed between the shaft 12 and thecomponent forming the bearing receiver 15 is connected to the spacedelimited by the motor housing 7 via a channel 24 in a region of theupper bearing 13 which is conductingly connected to the bore 20.

[0025] A rotating axial face seal ring 25 bears at the end-face on thestationary axial face seal ring 21, it is seated within the shaftshoulder and rotates with the shaft 12.

[0026] The thus formed axial face seal 18 seals the rotor space 17 tothe remaining split tube space, a corresponding sealing is provided atthe other side of the rotor 11.

[0027] On starting the pump the rotor space 17 may be completely orpartly filled with delivery fluid. As soon as the rotational speed ofthe motor increases the fluid located in the rotor space is heated,until finally the fluid evaporates and the pressure within the rotorspace 17 rapidly increases. If the limit pressure formed by the axialface seal 18 and determined by the pressure force of the spring 23 isexceeded, the stationary axial face seal ring lifts from the rotatingaxial face seal ring 25, thus moves upwards in the representationaccording to FIG. 1, by which means the rotor space 17 is conductinglyconnected via the channel 24 to the space surrounding the bearing 13.The rotor space is automatically emptied via the axial face seal 18 byway of the pressure formed in the rotor space 17 until finally onlyvapor is located in the rotor space and no fluid. The motor thenfunctions quasi as a dry-running motor. The operational rotational speedof such a motor may for example lie between 40,000 and 100,000revolutions per minute. The described procedure is repeated with eachstart of the motor as long as the rotor space 17 is again filled withfluid.

[0028] In order to ensure as complete as possible removal of the fluidfrom the rotor space 17 at the end-face of the rotor 11 there isprovided a co-running first displacement body 26 which is arranged atthe end-face of the rotor, as well as a second stationary displacementbody 27 which via an O-ring 28 bears tightly on the split tube 10. Thedisplacement bodies 26 and 27 are formed of heat-insulating plastic andhave essentially two tasks. On the one hand they are to extensively fillthe space remaining in the rotor space 17 between the rotor 11 and thebearing receiver 15 in order to minimize the free volume of the rotorspace 17 and thus the possible fluid accommodation of this. On the otherhand these bodies 26 and 27 represent insulation bodies which insulatethe rotor space 17 which is hot on operation, from the remaining bearingspace in order thus to avoid a formation of condensation in this regionand thus an increased friction. The formation and arrangement of theaxial face seal 19 arranged on the other side of the rotor 11corresponds functionally to the construction described with regard toaxial face seal 18. Here too there are provided displacement bodies 26and 27. Due to the design, the removal of the fluid from the rotor space17 may be effected via one or both of the axial face seals 18 and 19.Preferably however this is effected via the upper axial face seal 18,since here via the bore 12 there prevails only the suction-sidepressure, whereas the pressure-side pressure prevails at the other axialface seal 19 which must be overcome on removal of the fluid from therotor space.

[0029] With the above-described embodiment example the heating andevaporation of the fluid located in the rotor space is effectedautomatically as soon as suitable rotational speed regions have beenreached. According to the invention however one may provide anadditional electrical or other type of heating, thus in particular thesplit tube may be heated in the region outside the rotor 12, thus wherethe displacement bodies 26 and 27 are arranged. Also instead of theaxial face seal one may provide a pressure relief valve at a suitablelocation in the rotor space, for example in the split tube in order toremove fluid. The motor represented in the embodiment example is a d.c.motor, however one may also employ a.c. motors or high-rate motors.

1. A method for operating a pump unit with a centrifugal pump and withan electric motor driving this, whose rotor (11) runs in a split tube(10) which separates the rotor space (17) with respect to the stator (9)in a fluid-tight manner, wherein during and/or after running up themotor to an operational rotational speed the fluid located in the rotorspace (17) is at least partly removed.
 2. A method according to claim 1,wherein the fluid located between the rotor (11) and the split tube (10)is evaporated by the effect of heat.
 3. A pump unit, in particular foroperating according to a method according to claim 1 or 2, with acentrifugal pump and with an electric motor driving this, whose rotor(11) runs in a split tube (10) which separates the rotor space (17) withrespect to the stator (9) in a fluid-tight manner, wherein there areprovided means (18, 19, 23) which seal the rotor space (17) with respectto the delivery fluid in a pressure-limited manner.
 4. A pump unitaccording to claim 3, wherein the bearings (13, 14) carrying the rotor(11) are arranged outside the rotor space (17).
 5. A pump unit accordingto one of the preceding claims, wherein at least one bearing (13, 14)carrying the rotor (11) is arranged within the split tube (10).
 6. Apump unit according to one of the preceding claims, wherein both shaftends are led out of the rotor space (17), wherein an impeller (15) isprovided at one shaft end and wherein the fluid to be removed is ledaway near to that end of the shaft distant to the impeller (5).
 7. Apump unit according to claim 1, wherein the means sealing the rotorspace (17) with respect to the delivery fluid in a pressure limitedmanner are formed by way of at least one axial face seal (18, 19).
 8. Asubmersible pump unit according to one of the preceding claims, whereina bearing (13, 14) accommodating the shaft (12) of the rotor (11) isseated in a bearing receiver (15, 16) which is incorporated into thesplit tube (10), and wherein the axial face seal (18, 19) is arrangedbetween the rotor (11) and a bearing receiver (15, 16).
 9. A submersiblepump unit according to one of the preceding claims, wherein the bearingreceiver (15, 16) is sealed with respect to the split tube (10) by wayof an outer seal (28) and with respect to the stationary part (21) ofthe axial face seal (18, 19) by way of an inner seal (22).
 10. Asubmersible pump unit according to one of the preceding claims, whereinthe bearing receiver (15, 16) or the axial face seal (18, 19) bears withplay on the rotor (11) at the end-face, or there is provided a separatedisplacement component (26, 27) between the bearing receiver (15, 16)and the rotor (11) which reduces the free volume between the rotor (11)and the bearing receiver (15, 16) which may be filled by fluid inoperation.
 11. A submersible pump unit according to one of the precedingclaims, wherein the seals (22, 28) between the bearing receiver (15, 16)and the split tube (10) as well as between the bearing receiver (15, 16)and the stationary part (21) of the axial face seal (18, 19) are formedby O-rings (22, 28).
 12. A submersible pump unit according to one of thepreceding claims, wherein the bearing receiver (15, 16) and/or thedisplacement component (26, 27) consists of a heat-insulating material.13. A submersible pump unit according to one of the preceding claims,wherein the split tube (10) is heatable at least in a part region.
 14. Asubmersible pump unit according to one of the preceding claims, whereinthe split tube (10) is electrically heatable.
 15. A submersible pumpunit according to one of the preceding claims, wherein the split tube(10) is inductively heatable, in particular by the magnetic field formedbetween the rotor (11) and the stator (9) in operation.
 16. Asubmersible pump unit according to one of the preceding claims, whereinthe motor is a permanent magnet motor.